Cholesteryl ester-transfer protein (CETP) is an important player in metabolism of lipoproteins such as, for example, a high density lipoprotein (HDL). CETP is a 70 kDa plasma glycoprotein that is physically associated with HDL particles. It facilitates the transport of cholesteryl ester from HDL to apolipoprotein B-containing lipoproteins. This transfer is accompanied by transfer of triglycerides in the opposite direction. Thus, a decrease in CETP activity can result in an increase in the level of HDL cholesterol and a decrease in the level of very low density lipoprotein (VLDL) and low density lipoprotein (LDL). CETP can therefore simultaneously affect the concentrations of pro-atherogenic (e.g., LDL) and anti-atherogenic (e.g., HDL) lipoproteins.
Human and clinical studies have shown that inhibitors of CETP can be effective in elevating HDL levels by 30-60%. And, epidemiological studies have shown that decreased high-density lipoprotein cholesterol (HDL-C) is a powerful risk factor for coronary artery disease (CAD). Gordon et al., Circulation, 79, pp. 8-15, 1989; Despres et al., Atherosclerosis 153: 263-272, 2000. Elevating HDL-C has been shown to decrease this risk and it is estimated that each 1 mg/dl (0.02 mmol/l) elevation of HDL-C is associated with a 2-3% reduction in coronary heart disease (CHD) risk, a magnitude comparable to that for low density lipoprotein (LDL) lowering. It has been recommended that serum HDL-C levels of >40 mg/dl be considered as a therapeutic target in primary and secondary prevention. This goal appears to be particularly important in patients with low serum HDL-C levels and ischemic heart disease (IHD) or its equivalents, even if the therapeutic target for serum low-density lipoprotein cholesterol (LDL-C) levels (<100 mg/dl) has been achieved.
It is believed that the anti-atherogenic role of HDL is in part due its ability to promote the efflux of free cholesterol from cells and to transport it to the liver, a process termed reverse cholesterol transport. HDL could protect against atherosclerosis by several other mechanisms. For example, several studies showed HDL to have antioxidant and anti-inflammatory effects. Oxidative products of lipid metabolism induce inflammatory cell recruitment in vascular cells. HDL particles carry enzymes that retard LDL oxidation, including paraoxonase, platelet-activating factor acetylhydrolase, and lecithin-cholesterol acyltransferase. These enzymes degrade pro-inflammatory, oxidized phospholipids, limiting their accumulation in LDL. In addition, apoA-I can bind oxidized lipids and remove them from LDL. Further, HDL also can act as a carrier vehicle for small molecules, including bacterial lipopolysaccharide (LPS) thus regulating the inflammatory effects of LPS. In animal models of endotoxic shock, HDL attenuates organ injury and adhesion molecule expression. Thus elevating HDL is not only anti-atherogenic but it could also potentially be anti-inflammatory.
Existing therapies such as, for example, HDL-elevating therapies and anti-atherosclerosis therapies have limitations including serious toleration issues. There is a present need to find alternative therapies including methods of preventing or treating conditions or diseases associated with lipoprotein metabolism such as, for example, atherosclerosis.